Method of preparing diazo photolithographic plates



United States Patent 9 lVlETHOD OF PREPARING DIAZO PHOTO- LITHOGRAPHICPLATES Wilhelm Neugebauer, Wiesbaden-Biebrich, Jakob Barthenheier,Eddersheim on Main, and August Rebenstock, Wiesbaden-Biebrich, Germany,assignors, by mesne assignments, to Azoplate Corporafion, Summit, N. 1.,a corporation of New Jersey No Drawing. Application March 2, 1951,Serial No. 213,679

Claims priority, application Germany August 12, 1950 13 Claims. (Cl.955.4)

This invention relates to a process for fixing lithographic plates. Thefixing process of the present invention relates particularly to thefixing of lithographic plates prepared from a type of light sensitivematerial which has been put on the market only recently. This lightsensitive material consists of a layer of a light sensitive diazocompound coated on a base. To form the lithographic plates, the lightsensitive material is exposed to light through a master. The diazocompound is decomposed into a greasy ink receptive substance in thelight struck areas. Thus positive ink receptive images are obtained fromnegative masters and vice versa negative ink receptive images areobtained from positive masters.

Diazo compounds which are especially suitable in the light sensitivelayer for this type of photosensitive material are the condensationproducts of diazo-dlarylamines with formaldehyde. Cellulose acetatefoils which have been saponified on their surface may be used as thebase material. It is not necessary to add hardenable colloids such asglue to the light sensitive layer since the light decomposition productsof these diazo compounds are in themselves ink receptive.

The undecomposed diazo compounds are not ink receptive but neverthelessit is necessary to remove them from the areas which have not been struckby light or to fix the plate in some other manner. If this is not done,the diazo compound in these areas will become partially decomposedduring use of the plate so that these areas will gradually scum up andaccept more and more of the greasy" ink. It has been the practice towash the undecomposed diazo compound from these lithographic printingplates with water. Treatment with sodium throsulfate has also beenproposed. These procedures have not, however, proven fully satisfactoryin practice. The removal of the last remnants of the undecomposed diazocompound by washing with water is difiicult, and even washing for a longtime does not guarantee the complete removal of the undecomposed diazocompound. Neither does the treatment with thiosulfate result in anentirely satisfactory fixation. In these cases a strong tendency to scumdevelops more or less quickly during printing operations.

It has now been found that it is possible to fix lithographic plateswhich have been produced from light sensitive materials of the typedescribed by treating the material, after its exposure behind a master,with a solution of a water soluble azo coupling component which containshydrophilic groups and which will react with the remaining undecomposeddiazo compound to form a hydrophilic azo dye which does not accept thegreasy ink. It may be desirable to Wash the exposed plate with waterbefore treating it with the fixing solution which contains an azocoupling component in order to remove some or most of the undecomposeddiazo compound.

It is advantageous using a solution of pH not greater than 9.0 becausemore alkaline solutions tend to soften the saponified surface ofcellulose acetate foils so that they are more subject to damage.Furthermore, if the solution is not strongly alkaline, it is notnecessary to wash it off the plate before installing the plate on thepress and running the plate on the press with the fountain solutionwhich is generally acid.

2,702,242 Patented Feb. 15, 1955 The new fixing process rendersinnocuous the remnants of the diazo compound which were not decomposedduring the exposure by reason of their having been protected by theopaque parts of the master.

Azo coupling components containing sulfonic groups are especially wellsuited for this procedure. Those coupling components of high couplingenergy are of particular advantage, since such energy permits theircoupling to form azo dyes without the use of alkali. For example,sulfonic acids of compounds belonging to the pyrazolone series or theirsalts are very suitable; e. g.1-(4'-sulfophenyl)-3-methyl-pyrazolone-(5), or its salts. Good resultsare also obtained for example with 2,3-dihydroxynaphthalene 6 sulfonicacid, 1,8 dihydroxynaphthalene 4 sulfonic acid, 1,5 dihydroxynaphthalene3,7 disulfonic acid, 1,8 dihydroxy -naphthalene- 3,6 disulfonic acid, 1amino 8 dihydroxynaphthalene 3,6 disulfonic acid (H-acid), or with thesalts of these acids. Although it does not contain a sulfonic group,phloroglucinol may also be used as an azo coupling component accordingto the present invention. However, it should preferably be used in theform of a freshly prepared solution.

The hydrophilic azo coupling components to be used according to thisinvention are generally applied in the form of aqueous solutions. Otheringredients may be added to these solutions, for example,coupling-accelerating agents, buffer salts, glycerin, triethyleneglycol, and other water-soluble softeners.

The following examples are inserted to illustrate the present invention:

(1) A superficially saponified cellulose acetate foil, saponified to adepth of 5 to 7 microns is coated with an aqueous solution containingthree percent of the zinc chloride double salt of the condensationproduct of 1 mol of 4-diaZodiphenyl-amine with 1 mol of formaldehyde anddried. This condensation product may be produced in sulfuric acid of 60B. The light sensitive material is exposed to light under a negativemaster. The exposed material is then treated with a solution of a pH ofabout 6.8 that has been produced by dissolving in cc. of water, 5 g. of1-(4'-sulfophenyl)-3-methylpyrazolone-(S), 5 g. of trisodium phosphate,and 10 g. of triethylene glycol. Finally, the fixed plate is inked on anoffset lithographic printing machine. A positive printing plate is thusobtained which is not affected by further exposure to light. It is notnecessary to rinse or wash oif the plate after treatment with the fixingsolution because the pH of the fixing solution is on the acid side ofthe neutral point.

(2) A superficially saponified cellulose acetate foil, rendered lightsensitive as described in Example 1, is exposed to light under anegative master and then washed with water. In order to achieve acomplete coupling of the remaining diazo compound there is applied anaqueous solution of a pH of about 8.4 containing five percent of sodium2,3 dihydroxynaphthalene 6 sulfonate, one half percent of soda, and tenpercent of glycerin. The plate is finally prepared for the pressaccording to the procedure of Example 1.

The fixing of the plate can also be carried out after the plate has beeninstalled on the press. One method of doing this is to add the couplingcomponent to the fountain solution.

Having thus described our invention what is claimed is:

1. The process of forming lithographic printing plates from a saponifiedacetate foil coated with an ink repellent diazo compound whichdecomposes into a greasy ink receptive substance upon exposure to lightsaid compound being obtained by the condensation of diazo-diarylaminewith formaldehyde, comprising the steps of exposing said foil to a lightimage, treating the foil after exposure to light with an aqueoussolution containing a water soluble azo coupling component of highcoupling energy containing hydrophilic groups which couples with theundecomposed diazo compound in the unexposed areas to form an inkrepellent dye, and thereafter apply ing ink in the presence of water tosaid foil.

2. The process of forming lithographic printing plates from a saponifiedacetate foil coated with an ink repellent diazo compound obtained by thecondensation of a diazo-diarylamine with formaldehyde and whichdecomposes into a greasy ink receptive substance upon exposure to lightcomprising the steps of, exposing said foil to a light image, treatingthe plate after exposure to light with an aqueous solution containing anazo coupling component of the pyrazolone series of high coupling energycontaining hydrophilic groups which couples with the undecomposed diazocompound in the unexposed areas to form an ink repellant dye, andthereafter applying ink in the presence of water to said foil.

3. The process of forming lithographic printing plates from a saponifiedacetate foil coated with the condensation product of an ink repellentdiazo-diarylamine with formaldehyde which decomposes into a greasy inkreceptive substance upon exposure to light comprising the steps of,exposing said material to a light image, treating the plate afterexposure to light with an aqueous solution containing an azo couplingcomponent selected from the group consisting of compounds of thepyrazolone series of high coupling energy containing a sulfonic acidgroup and their salts which couples with the undecomposed diazo compoundin the unexposed areas to form an ink repellant dye, and thereafterapplying ink in the presence of water to said foil.

4. The process of forming lithographic printing plates from a saponifiedacetate foil coated with the condensation product of an ink repellentdiazo-diarylamine with formaldehyde which decomposes into a greasy inkreceptive substance upon exposure to light comprising the steps of,exposing said material to a light image, treating the plate afterexposure to light with an aqueous solu' tion containing an azo couplingcomponent selected from the group consisting of high energy componentscontaining a sulfonic acid group and their salts which couples with theundecomposed diazo compound in the unexposed areas to form an inkrepellant dye, and thereafter applying ink in the presence of Water tosaid foil.

5. The process of forming lithographic printing plates from a saponifiedacetate foil coated with the condensation product of an ink repellentdiazo-diarylamine with formaldehyde which decomposes into a greasy inkreceptive substance upon exposure to light comprising the steps of,exposing said material to a light image, treating the plate afterexposure to light with an aqueous solution containing an azo couplingcomponent selected from the group consisting of dihydroxy-naphthalenesulfonic acids and their salts which couples with the undecomposed diazocompound in the unexposed areas to form an ink repellant dye, andthereafter applying ink in the presence of water to said foil.

6. The process of forming lithographic printing plates from a saponifiedacetate foil coated with the condensation product of an ink repellentdiazo-diarylamine with formaldehyde which decomposes into a greasy inkreceptive substance upon exposure to light comprising the steps of,exposing said material to a light image, treating the plate afterexposure to light with an aqueous solution containing an azo couplingcomponent selected from the group consisting of2,3-dihydroxynaphthalene-6-sulfonic acid and its salts which coupleswith the undecomposed diazo compound in the unexposed areas to form anink repellant dye, and thereafter applying ink in the presence of waterto said foil.

7. The process of forming lithographic printing plates from a saponifiedacetate foil coated with the condensation product of an ink repellentdiazo-diarylamine with formaldehyde which decomposes into a greasy inkreceptive substance upon exposure to light comprising the steps of,exposing said material to a light image, treating the plate afterexposure to light with an aqueous solution containing an azo couplingcomponent selected from the group consisting of1,5-dihydroxynaphthalene-3,7-disulfonic acid and its salts, andthereafter applying ink in the presence of water to said foil.

8. The process of forming lithographic printing plates from a saponifiedacetate foil coated with the condensation product of an ink repellentdiazo-diarylamine with formaldehyde which decomposes into a greasy inkreceptive substance upon exposure to light comprising the steps of,exposing said material to a light image, treating the plate afterexposure to light with an aqueous solution containing an azo couplingcomponent selected from the group consisting of1,8-dihydroxynaphthalene-3,6-disulfonic acid and its salts, andthereafter applying ink in the presence of water to said foil.

9. The process of forming lithographic printing plates from a saponifiedacetate foil coated with the condensation product of an ink repellentdiazo-diarylamine with formaldehyde which decomposes into a greasy inkreceptive substance upon exposure to light comprising the steps of,exposing said material to a light image, treating the plate afterexposure to light with an aqueous solution containing an azo couplingcomponent selected from the group consisting ofl,8-dihydroxynaphthalene-4-sulfonic acid and its salts, and thereafterapplying ink in the presence of water to said foil.

10. The process of forming a lithographic printing plate from asaponified acetate foil having a surface thereof coated with an inkrepellent diazo compound which decomposes into a greasy ink receptivesubstance upon exposure to light obtained by the condensation of adiazodiarylamine with formaldehyde comprising the steps of exposing thecoated surface of said foil to a light image, after exposure treatingsaid coated surface with an aqueous solution containing a sulfonatedphenylmethyl pyrazolone which couples with the undecomposed diazocompound in the unexposed areas to form an ink repellant dye, andthereafter applying ink on said coated surface in the presence of water.

11. The process of forming a lithographic printing plate from asaponified acetate foil having a surface thereof coated with an inkrepellent diazo compound obtained by the condensation of adiazo-diarylamine with formaldehyde comprising the steps of, exposingthe coated surface of said foil to a light image whereby those areas ofsaid coated surface which are struck by light become ink receptive andthe remaining areas of said coated surface are unafiected, treating atleast said remaining areas with an aqueous solution of a sulfonatedphenylmethyl pyrazolone to prevent said remaining areas from becomingink receptive and thereafter applying ink in the presence of water onsaid areas struck by light.

12. The process of forming a lithographic printing plate from asaponified acetate foil having a surface thereof coated with thecondensation product of an ink repellent diazo-diarylamine withformaldehyde comprising the steps of, exposing the coated surface ofsaid foil to a light image whereby those areas of said coated surfaceWhich are struck by light become ink receptive and the remaining areasof said coated surface are unaffected, treating the plate after exposureto light with an aqueous solution containing an azo coupling componentselected from the groups consisting of the sulfonic acids of thepyrazolone series, the sulfonic acids of p'oly-hydroxynaphthalenes andthe sulfonic acids of amino-hydroxynaphthalene to prevent said remainingareas from becoming ink receptive, and thereafter applying ink in thepresence of water on said areas struck by light.

13. The process of forming a lithographic printing plate from asaponified acetate foil having a surface thereof coated with thecondensation product of an ink repellent diazo-diarylamine withformaldehyde comprising the steps of, exposing the coated surface ofsaid foil to a light image whereby those areas of said coated surfacewhich are struck by light become ink receptive and the remaining areasof said coated surface are unalfected, treating at least said remainingareas with an aqueous solution containing an azo coupling componentselected from the group consisting of 1-(4'-sulfophenyl)- 3-methylpyrazolone-(5)- and its salts to prevent said remaining areas frombecoming ink receptive, and thereafter applying ink in the presence ofwater on said areas struck by light.

References Cited in the file of this patent UNITED STATES PATENTS2,063,631 Schmidt Dec. 8, 1936 FOREIGN PATENTS 337,868 Great BritainNov. 13, 1930 402,737 Great Britain 1933 624,472 Great Britain Iune'9,1949 904,255 France Oct. 31, 1945

1. THE PROCESS OF FORMING LITHOGRAPHIC PRINTING PLATES FROM A SAPONIFIEDACETATE FOIL COATED WITH AN INK REPELLENT DIAZO COMPOUND WHICHDECOMPOSES INTO A GREASY INK RECEPTIVE SUBSTANCES UPON EXPOSURE TO LIGHTSAID COMPOUND BEING OBTAINED BY THE CONDENSATION OF DIAZO-DIARYLAMINEWITH FORMALDEHYDE, COMPRISING THE STEPS OF EXPOSIING SAID FOIL TO ALIGHT IMAGE, TREATING THE FOIL AFTER EXPOSURE TO LIGHT WITH AN AQUEOUSSOLUTION CONTAINING A WATER SOLUBLE AZO COUPLING COMPONENT OF HIGHCOUPLING ENERGY CONTAINING HYDROPHILIC GROUPS WHICH COUPLES WITH THEUNDECOMPOSED DIAZO COMPOUND IN THE UNEXPOSED AREAS TO FORM AN INKREPELLENT DYE, AND THEREAFTER APPLYING INK IN THE PRESENCE OF WATER TOSAID FOIL.